Multi-zone fixed-bed or moving-bed reactor with an integrated heat exchanger

ABSTRACT

This invention relates to a staged-zone reactor of the axial-flow type that makes it possible to implement strongly endothermic or exothermic reactions. The reactor comprises a constriction of the catalytic bed between an upper zone ( 3   a ) and a lower zone ( 3   b ), making it possible to house in the reactor a heat exchanger for the intermediate heating or cooling of the effluents. Process of chemical conversion using this reactor for exothermic or endothermic reactions in the gas and/or liquid phase, and in particular for the oligomerization reaction of C2 to C12 fractions for the purpose of producing a diesel fraction.

FIELD OF THE INVENTION

This invention relates to a reactor inside of which is carried out atleast one catalytic reaction that has a significant thermal effect,generally a release of heat (so-called exothermic reactions) orsometimes an absorption of heat (so-called endothermic reactions).

It also relates to a process for oligomerization of olefinic feedstocks(i.e., a polymerization or addition that is limited to essentially 2 to6 monomers or molecules that are basic). It also relates in particularto the reactions for adding an olefin to another compound that ispresent in the feedstock, for example an olefin, a sulfur-containingcompound, a nitrogen-containing compound, an aromatic molecule, wherebysaid addition reactions are aimed at increasing the molecular weight ofthis compound.

It relates more particularly to the oligomerization reactions startingfrom olefinic hydrocarbon fractions that contain 2 to 12 carbon atoms,preferably 3 to 7 carbon atoms, and more particularly 4 to 6 carbonatoms, whereby the oligomerization reactions make it possible to producefractions of gasoline, diesel or lubricant, and more particularlyhydrocarbons of the diesel fraction.

The invention relates to a reactor with several reaction zones, stackedvertically and separated by at least one heat exchange zone at aconstriction of the catalyst path between the reaction zones.

BACKGROUND

It is known in the prior art to carry out chemical reactions, inparticular for refining petroleum fractions or hydrocarbons, incatalytic reactors that use a granular bed. Generally, catalyst grainsof a characteristic size between 0.5 and 5 mm are used. These catalystgrains often have an essentially spherical shape to facilitate theirflow. They can, however, have another shape, for example if they areproduced by extrusion. The catalysts that are used in the reactoraccording to the invention are all catalysts that have a characteristicsize (for example, a diameter) of between 0.5 and 5 mm in diameter, andpreferably between 1 to 4 mm.

In general, the deactivation of catalysts, and, for example, that ofcatalysts that comprise a zeolite used for the purpose of the productionof diesel fractions by oligomerization, is fast. It is thereforenecessary to initiate a replacement of the catalyst regularly so as tomaintain the performance levels of the reactor in terms of selectivityand output.

Two types of technology are commonly used for this purpose:

In the “fixed-bed” technology, all of the catalyst that is contained inthe reactor at the end of a cycle is changed when the consumption of thecatalyst is considered to be spent. The operation is then typically cutoff, the reactor is emptied, and then it is filled again by the newand/or regenerated catalyst.

Another type of technology is used for catalytic reactions withcirculation (continuous or semi-continuous) and regeneration (continuousor semi-continuous) of the catalyst: that of the “moving bed” thatconsists of a stack of catalyst grains contained in the reactor, as in afixed bed, but said grains moving (at a very slow average speed,continuously or intermittently) from the top to the bottom of thereactor under the effect of the force of gravity. At the bottom of thereactor, a small amount of spent catalyst is drawn off continuously orintermittently, and the same amount of new catalyst and/or regeneratedcatalyst is introduced at the top of the reactor. It is possible, forexample, to draw off and to reintroduce a suitable amount of catalystevery 4 or 8 hours such that the overall activity of the catalystremains constant. The spent catalyst that is drawn off is typicallyregenerated and then recycled, optionally except for a small amount ofcatalyst that is eliminated and replaced by new catalyst.

The reactor according to the invention can be used both in a fixed bedand in a moving bed, this second variant of implementation representing,however, the preferred variant.

Furthermore, for the reactions with strong endothermicity or with strongexothermicity, means for heat exchange with the reaction fluid (furnaceor heat exchanger) are sometimes used inside or outside the reactor soas to maintain the temperature difference between the inlet and theoutlet of the reactor within desired limits and/or to reset thetemperature of the reaction fluid between two or more reactors that arearranged in a series.

Patent US 2002/0011428 A1 describes a multi-staged moving-bed reactorthat is intended to implement hydrotreatment reactions. One system,subject of other patents (in particular patent U.S. Pat. No. 5,076,908),makes it possible to add and to withdraw catalyst continuously orsemi-continuously from each stage of the reactor. The feedstock flowsfrom one stage to the next. By contrast, the catalyst of one stage doesnot flow into the next stage. It was found that such a system can alsobe used to implement an oligomerization reaction. The described system,however, does not make it possible to effectively monitor thetemperature profile within each reaction section.

Patent WO 02/04575 describes a process for oligomerization on a zeoliteimplementing a tubular-type reactor, in a fixed bed, or any otherreactor that can be used so as to carry out the oligomerizationreaction. The patent describes a method that makes it possible to addand to withdraw the catalyst continuously or semi-continuously from thereactor. By contrast, the problem of monitoring the exothermicity of thereaction is not addressed.

Patent EP 1236506A1 describes a multi-staged reactor with a small bedthickness with an internal heat exchanger, used primarily within theframework of reactions for dehydrogenating long paraffins. This systemmakes it possible to monitor specifically the temperature within eachreaction section. In contrast, it is hardly suitable for implementinglarge amounts of catalyst, being suitable for small bed thicknesses. Thecatalyst filling rate in the reactor is very low here.

The above-mentioned patent applications that describe superposed ormulti-staged reactors therefore do not describe means that make itpossible both to use large amounts of catalyst and to implementintegrated thermal means.

This invention describes a reactor and a process for chemical conversionof hydrocarbons that uses this reactor, making it possible to optimallyresolve the problems that are linked to the implementation of stronglyexothermic or endothermic reactions, in particular oligomerizationreactions. It makes it possible to implement a compact reactor, having alarge capacity for what the amount of catalyst present is and having,moreover, an inside volume that is noteworthy for the integration of aheat exchanger.

SUMMARY DESCRIPTION OF THE INVENTION

This invention will be illustrated in the particular case of anexothermic reaction for oligomerization of olefins within an olefinicfeedstock (often comprising 20% to 100% by weight of olefins). Its fieldof application, however, is more extended and relates to all exothermicor endothermic reactions in gas phase and/or liquid phase for whichtypically a noteworthy catalytic volume and a thermal control areessential, in particular the reactions for addition of an olefin toanother compound that is present in the feedstock, for example anolefin, a sulfur-containing compound, a nitrogen-containing compound, oran aromatic molecule, whereby said addition reactions aim at increasingthe molecular weight of this compound.

In particular, this reactor is particularly suitable for theimplementation of a reaction for oligomerization of olefinic hydrocarbonfractions that contain 2 to 12 carbon atoms, preferably 3 to 7 carbonatoms, and more preferably also 4 to 6 carbon atoms, making it possibleto obtain hydrocarbons within the range of gasoline, diesel orlubricating oil fractions, and more particularly hydrocarbons of thediesel fraction of the typical distillation interval encompassed between160 and 370° C., in particular between 200 and 365° C.

It is desirable, for this chemical reaction, to avoid importantdisparities of the catalytic activity between the different reactionzones that generate conversion losses.

In addition, the oligomerization reaction is strongly exothermic. Toohigh a temperature promotes the cracking reactions of oligomerizedcompounds and is therefore not desirable.

Too low a temperature in some reaction zones limits the conversion intoadequately heavy compounds that are sought in the composition of adiesel fraction. It is therefore desirable to monitor the temperatureswithin various reaction zones specifically. In particular, it isadvantageous to adjust the temperature level of a catalytic reactionzone based on the activity of the catalyst within said zone.

For these different reasons, it is desirable to implement severalsuccessive reaction zones, preferably with noteworthy or significantcatalyst volumes, and to install heat exchange means making it possibleto adjust the reaction fluid temperature between two successive zones.

To solve the above-mentioned technical problems, the invention proposesa reactor that has a noteworthy or significant catalytic volume,integrated heat exchange means, at a constriction in the path of acatalyst. In a preferred variant, the reactor according to the inventioncomprises means that make possible an implementation in a moving bed.

According to an optional characteristic arrangement, the reactor cancomprise means that make it possible to implement, typically at theinlet of each reaction zone, an added portion of fresh or regeneratedcatalyst for its mixing with at least a portion of the (partially) spentcatalyst that is obtained from the upstream reaction zone.

The invention also proposes a process for carrying out chemicalreactions in this reactor, in particular a process for oligomerizationof olefinic feedstocks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a view of the reactor according to the invention in itsbasic configuration.

FIG. 2 shows a view of the reactor according to the invention in avariant that comprises an injection of an additional reaction fluidbetween two reaction zones.

DETAILED DESCRIPTION OF THE DRAWINGS

The invention will be better understood in reference to FIGS. 1 and 2that illustrate different embodiments of the invention without, however,limiting its scope.

The invention is illustrated in its basic configuration by FIG. 1.

In a general form, the invention relates to a reactor of elongated shapealong an essentially vertical axis, whereby this reactor comprisesseveral vertically-staged catalytic reaction zones in the samecylindrical shell, whereby this reactor is adapted to the axialcirculation of the reaction fluid that is arranged in a series in eachof these zones and comprises means (100) for introducing and means (101)for evacuating said reaction fluid, means (102) for intake of fresh orregenerated catalyst at the top of the reactor, and means (105) forevacuating spent catalyst in the lower portion of the reactor, wherebythis reactor comprises in particular:

An upper reaction zone (3 a) that is filled with granular catalyst, witha section (in a horizontal plane) that is essentially identical to thatof the cylindrical shell on a portion of its height, directly connectedvia a constriction zone to a reaction zone (3 b) that is also filledwith granular catalyst and with a section that is essentially identicalto that of the cylindrical shell on a portion of its height, locatedjust below the upper reaction zone (3 a), whereby these reaction zones(3 a) and (3 b) are two successive reaction zones that are directlyconnected, on the one hand, by a reaction effluent path, and, on theother hand, by a catalyst path from zone (3 a) to zone (3 b) throughsaid constriction zone, whereby zone (3 a) is connected at its upperportion, directly or indirectly, to said means (102) for feeding freshor regenerated catalyst, whereby zone (3 b) is connected at its lowerportion, directly or indirectly, to said means (105) for evacuatingspent catalyst, whereby the reactor, located at the constriction zonebetween this constriction zone and the cylindrical shell of the reactor,also comprises a heat exchanger (8) for heating or cooling the reactionfluid that circulates between zones (3 a) and (3 b).

Zones (3 a) and (3 b) being filled with granular catalyst over a sectionthat is essentially identical to that of the cylindrical shell of thereactor over a portion of its height, they therefore have a highcatalytic volume. The constriction zone that allows the catalyst path tohouse an integrated exchanger in the reactor at this typically annularzone is advantageous, however.

In its lower portion, zone (3 a) preferably comprises an essentiallyconical convergent that comprises perforations for the path of reactionfluid, connected to a channel (2 b) with a small diameter relative tothat of the reactor, whereby this channel delimits at least a portion ofthe constriction zone into which the catalyst can flow (at the end ofeach cycle in a fixed bed; continuously or semi-continuously in a movingbed). This channel (2 b) typically has a diameter of between 1% and 50%of the diameter of the reactor at the constriction zone, preferablybetween 1% and 30%, and very preferably between 2% and 20%. A largeavailable space between the constriction zone and the cylindrical shellthat is advantageously used to install heat exchanger (8) resultstherefrom. Relative to the prior art, two advantages are broughttogether: the one linked to the use of large volumes of catalyst (thereaction zones that have the diameter of the reactor, in connection withaxial-reactor-type reaction zones, into which the reaction fluid flowsprimarily in an essentially parallel way to the vertical axis of thereactor), and the one of still being able to house an integrated heatexchanger, thanks to the constriction. Typically, heat exchanger (8) islocated around the constricted catalyst path.

The invention can relate both to a fixed-bed reactor and to a moving-bedreactor, even if use in a moving bed is preferred. In the case of afixed-bed reactor, all of the reaction zones are completely filled byregenerated and/or fresh catalyst, and the reactor is completely emptiedof all its catalyst when the latter, at the end of an operating cycle(in a fixed bed), is spent to such a point that its replacement isnecessary.

According to the invention, two zones (3 a) and (3 b) are successivereaction zones, which means that the effluents of one of these zonesfeed the other zone without passing through another reaction zone.

According to a variant of the invention, usable in a moving bed, thereactor that is shown in FIG. 1 comprises means for draw-off andevacuation (104) of a portion of the spent catalyst that is obtainedfrom upper reaction zone (3 a) connected to collecting means. This makesit possible to eliminate a portion (for example 10 to 70%, and often 15to 50% of the spent catalyst before the introduction of regeneratedand/or fresh catalyst.

Thus, the average activity of the catalyst in a mixture that supplies (3b) is increased, generally without significantly increasing the totalflow of catalyst entering into (3 b), and even by keeping the flow ofcatalyst that circulates in (3 a) and in (3 b) constant. With a constanttotal flow of fresh and/or regenerated catalyst, the invention makes itpossible to obtain a certain rebalancing of the catalytic activitybetween the different reaction zones.

This added portion of regenerated and/or fresh catalyst can alsorepresent, for example, from 10 to 70%, and often 15 to 50% of thecatalyst that supplies (3 a) to the top of the reactor or else thatsupplies (3 b).

Typically, two successive reaction zones (3 a) and (3 b) are connectedby a circuit for circulating reaction fluid that passes through heatexchanger (8) for heating or cooling this reaction fluid, whereby thiscircuit typically is established essentially around the constrictionzone, between this zone and the cylindrical shell of the reactor, in anintermediate zone that is located between two successive reaction zones(3 a) and (3 b). Optionally, according to a variant that is shown inFIG. 2, the intermediate zone comprises means (10) for introducing oneor more additional reaction fluids (106) and for mixing this or thesefluids with the reaction fluid that circulates between successivereaction zones (3 a) and (3 b). It may be useful in particular to add anew chemical reagent to carry out a reaction subsequent to the onecarried out in the upstream zone, for example a reaction for alkylationof an aromatic molecule or a mixture of aromatic compounds and/or forintroducing a hydrogen-rich recycling gas (comprising more than 50 mol %and often more than 70 mol % of H2) so as to increase the amount ofhydrogen present. This gas can also have a thermal effect, a heatingeffect or more frequently a cooling effect of effluents before theyreturn into the downstream reaction zone.

The reactor of the invention, and all its variants as described in thisapplication, can be used in particular within the scope of a process forchemical conversion of hydrocarbons, and in particular a process foroligomerization of olefinic feedstocks that have 2 to 12 carbon atoms,whereby this or these process(es) constitute another object of theinvention.

In such a process, in particular of oligomerization, the typicalconditions are as follows: the pressure is between 0.1 and 10 MPa andpreferably between 0.3 and 7 MPa, the temperature is between 40 and 600°C. and preferably between 60 and 400° C., the hourly volumetric flowrate VVH is between 0.01 and 100 h⁻¹ and preferably between 0.4 and 30h⁻¹ and the catalyst circulates in each reaction zone at a speed(average) of between 1 cm/hour and 200 cm/hour and preferably between 2cm/hour and 100 cm/hour.

The invention is particularly suited to processes in which the operatingconditions are selected: temperature, pressure VVH, so as to limit thetemperature variation within each of the reaction zones to one or morevalues of between 2° C. and 50° C. Heat exchanger (8) typically can coolthe reaction fluid (or heat it for an endothermic process) from 2 to 50°C., and preferably from 10 to 50° C.

DETAILED DESCRIPTION OF THE FIGURES

Reference is now made again to FIG. 1. In the reactor that is shown, thecatalyst passes through all of the reaction zones in a downward flow,and the feedstock (the reaction fluid) also passes through all thereaction zones but counter-current to the catalyst. The reaction zonesthat are shown are of the axial-reactor type. However, a configurationin which the reaction fluid would circulate at co-current of thecatalyst, i.e., from top to bottom, is also perfectly possible withinthe scope of the invention. Furthermore, the reaction zones can be ofthe radial-reactor type. An axial-reactor configuration is preferred,however.

The fresh and/or regenerated catalyst is supplied, primarily in general,to the top of the reactor via line (102), then tube (2 a). This catalystflows slowly, continuously or intermittently, into a zone (3 a),referenced (3 a) in FIG. 1, which is the upper reaction zone. At thelower portion of this zone, it is collected in a collecting zone (4 a),then it flows into chamber (5). A fraction of this catalyst, partiallyspent, is drawn off via tube (104), typically to be regenerated. Chamber(5) can be provided with means (not shown) for facilitating theextraction of a granular product such as the catalyst, for example anextracting screw, or a pneumatic transport drum, or a fluidized bed orany other means that is known to one skilled in the art. It is alsopossible to use a tube (104) that is inclined by at least 60° relativeto the horizontal line and optionally injections of aeration gas of thecatalyst (for example nitrogen) to facilitate the evacuation of thecatalyst.

The non-extracted portion of the catalyst that is present in chamber (5)flows into mixing chamber (7) to be mixed with another portion of thefresh and/or regenerated catalyst, introduced by line (103), via valve(6). It is possible to use a tube (103) that is inclined by at least 60°relative to the horizontal, including in its end portion, and optionallyinjections of aeration gas of the catalyst (for example nitrogen) tofacilitate the introduction of the fresh and/or regenerated catalyst.

Mixing chamber (7) can be provided with means (not shown) to facilitatethe mixing of fresh/regenerated catalyst and partially spent catalyst.It is possible in particular to use a rotating basket for stirring thecatalyst in zone (7) or else stirring blades that are located in zone(7) and moved via an external motor. It is also possible to use afluidized bed or any other known granule mixing system.

The thus formed mixture of catalysts has a catalytic activity that hasbeen increased relative to that of the spent catalyst that is obtainedfrom zone (3 a). This mixture passes through a constriction path (2 b)then supplies zone (3 b), referenced (3 b) in FIG. 1, which isimmediately less than (3 a) (from the viewpoint of reaction zones).

The spent catalyst that is obtained from zone (3 b) circulates in anextracting tube (4 b) then is evacuated from the reactor via tube (105)on which valve (9) is found. It is then sent to a regeneration zone (notshown) via a system for particle transport by means of a liquid orgaseous transport fluid (for example nitrogen), according to well-knowntechnologies of one skilled in the art relative to the moving bed. It ispossible in particular to use, at the level of tube (105) or below valve(9), a receiving flask for the spent catalyst that makes it possible tostore a determined amount of catalyst before its sequential evacuationvia pneumatic transport, generally by means of a primary fluid foraeration of the catalyst and a secondary transport fluid.

The technologies that make it possible to introduce, to extract, to mixor to transport granular products are generic technologies that are wellknown to one skilled in the art, to which the invention is not linked.

The regeneration zone of the catalyst, not shown, can be equipped with agas classifier or any other means that makes it possible to separate thefine particles that are created during various operations for transportof catalyst. The regenerated catalyst (in particular after a controlledoxidation of carbon deposits) is typically recycled via tubes (102) and(103) with an added portion of fresh catalyst. A fraction of thecatalyst of the loop (often spent catalyst) is generally evacuated tomake possible the addition of fresh catalyst by keeping constant thetotal amount of catalyst used.

The reaction fluid, for example a C4-C6 olefinic hydrocarbon feedstock(essentially having 4 to 6 carbon atoms), is fed via tube (100) intofeed chamber 1, passes through initial reaction zone (3 b) filled withcatalyst, then intermediate zone (22) that does not contain catalyst,then returns to final reaction zone (3 a) filled with catalyst, thenreturns into chamber (23) before being evacuated via tube (101).Reaction zones (3 a) and (3 b) are advantageously provided at the upperand lower portion with perforated grids (shown in dotted lines in thefigures) to make possible the path of reaction fluid. These grids can beinclined by an angle of 60° or more, in the lower portion, to facilitatethe flow of the catalyst. A heat exchanger (8) with thermal fluidcirculation is located inside the reactor in intermediate zone (22)(itself located inside the reactor) to carry out a heat exchange withthe reaction fluid that moves between (3 b) and (3 a). This heatexchanger is advantageously located at constriction 2 b of the catalystpath because of the space thus cleared inside the reactor.

This heat exchanger generally makes use of a thermal heating or coolingfluid that circulates inside tubes, all of the tubes forming, forexample, one or more pins extending into the reaction fluid inintermediate zone (22). The exchanger, however, can be of any type thatis known to one skilled in the art, for example a plate exchanger, orfin tube exchanger, or bare-tube or straight-tube exchanger, or anexchanger with a spiral wound around the vertical axis of the reactor(and typically of the constriction zone), whereby the invention is in noway limited to a particular technology of this exchanger.

Various pressurized fluids can be used as a thermal fluid for heating orcooling: water vapor, air, water, hydrogen or hydrogen-rich recyclinggas, nitrogen, molten salts, aromatic oil, the feedstock itself, etc.

FIG. (2) shows another reactor according to this invention, comprisingthe same elements as those of the reactor of FIG. 1. In addition, itcomprises a tube (106) for the addition of an additional reaction fluid,for an added portion of reagent and/or an added portion of hydrogen.This fluid is distributed into intermediate zone (22) via a distributionline (10) to facilitate its homogeneous mixing with the reaction fluidthat is obtained from zone (3 b). The mixing is also promoted by thefact that intermediate zone (22) is free of catalyst.

The advantages of the reactor(s) according to this invention relative tothe known reactors of the prior art are:

-   -   a clear improvement in performance levels (conversion,        selectivity, yield)    -   a more significant reliability of the installation due to the        simplicity and the compactness of the means used, in particular        heat exchange means that are implemented    -   the cost of the reactor and that of its installation are also        reduced because of its compactness.

A typical operation of the reactor of FIG. 1 is as follows: the flowrate of the added portion of regenerated catalyst or optionally freshcatalyst is defined so as to keep a determined level of activity on eachreaction zone. For example, this catalyst addition flow rate can bedefined based on a characteristic of the reaction fluid at the reactionzone outlet. This characteristic can be a temperature, a composition, aconversion, or any other physico-chemical characteristic that can bemeasured on line. The correlations that link one or more of these valuesthat can be measured on line and the activity level of the catalystdepend on the reaction that is implemented, the type of catalyst and itsspeed of circulation. A simple means is in particular to control theconversion in zone (3 b) or the temperature variation (delta T) of thereaction fluid in this zone, or else the outlet temperature of thiszone, by action on the supply flow rate of the regenerated and/or freshcatalyst: If the measured value of delta T is less than the value thatis provided (typically depending on the initial composition of thefeedstock), or if the value of the outlet temperature of the zonecorresponds to an inadequate reaction, the supply flow rate ofregenerated and/or new catalyst is increased in this zone, andconversely, the added portion is reduced if the conversion in the zone(deduced from delta T or the outlet temperature) is too significant. Itis possible to simultaneously evacuate the same amount of spent catalystas that of the added portion of catalyst before carrying out the mixingto keep constant the overall flow rate of catalyst in zone (3 b).

The flow rate of the added portion of catalyst can therefore be entirelyautomated. Alternatively, it is possible to be adjusted at certain times(for example once or twice per day) by the operator, based ontemperatures and/or the above-mentioned delta T in particular.

The heating or cooling of reaction fluid in exchanger (8) (delta T) canbe controlled in particular by the flow rate or the temperature level ofthe thermal fluid that circulates in exchanger (8).

The reactor of FIG. 2 operates analogously. In this reactor, an addedportion of reagents and/or hydrogen that is fed by tube (106) is used.This added portion typically has a controlled flow rate and temperature.

The catalyst that circulates in the reactor according to the inventioncan be of various types. In the case of an oligomerization reactor, itis possible to use in particular any type of acid catalyst that allowsthe oligomerization, for example an amorphous silica-alumina-typecatalyst or a solid phosphoric acid-type catalyst or an ion exchangeresin-type catalyst, or then a catalyst that exhibits a selectivity ofshape, for example a zeolitic catalyst, for example a zeolitic catalystof the structural type MFI, FER, EUO, TON, LTL, MOR, MTT, MEL, MWW, MTWor the zeolites NU-86, NU-87, NU-88 and IM-5.

These zeolitic acid catalysts can be used as is or after modifications,whereby said modifications preferably affect the acidity of thecatalyst, and whereby the term acidity designates both the inherentforce of the acid sites and the concentration of acid sites.

These modifications can affect the framework of the zeolite, forexample, if it is a dealuminification by steam treatment or by acidtreatment, and/or affect the surface of the zeolite, for example (i) byexchanges of protons by cations of alkaline types, (ii) by inert phasedeposits on the surface of zeolites.

The preferred operating conditions are those that are used in a standardmanner for the oligomerization of olefins by catalysts of acid solidtype:

-   -   a temperature of between 100° C. and 300° C.    -   a pressure of between 0.1 and 7 MPa    -   a VVH (volumetric flow rate expressed as the ratio of the        volumetric flow rate of feedstock to the catalyst volume        contained in the reaction zone) of between 0.01 and 100 h⁻.

The reactor according to the invention is particularly suited to olefinoligomerization reactions, but it can be used more generally for anytype of exothermic or endothermic reaction, taking place in gas and/orliquid phase, and for which a fine control of the temperature profile ineach reaction zone is necessary, in particular the reactions foraddition of an olefin to another compound that is present in thefeedstock, for example an olefin, a sulfur-containing compound, anitrogen-containing compound, an aromatic molecule, said additionreactions being aimed at increasing the molecular weight of thiscompound, in particular the reactions for alkylation of thiopheniccompounds by olefins, the metathesis of olefins. The reactor accordingto the invention can also be used for the skeletal isomerizationreactions of light olefins, such as, for example, the olefins with 4 or5 carbon atoms.

In the case of exothermic reactions, the thermal fluid of cooling(coolant) can be any fluid that is suitable for carrying out the heatexchange under good conditions, in particular by observing a meantemperature difference between the reaction fluid and the cooling fluidof at least 5° C. and preferably at least 10° C.

The invention is in no way tied to a particular cooling or heatingfluid.

Example According to the Invention:

This example relates to the reaction of oligomerization of anunsaturated C3 fraction on a bed in a reactor according to theinvention, such as the one of FIG. 1.

The reactor comprises two reaction zones denoted as (3 b) (initial zone(3 b)) and (3 a) (final zone (3 a)), in a series, separated by anintermediate zone that comprises a water cooling system that constitutesheat exchanger (8).

The feedstock and the catalyst circulate at counter-current.

A dealuminified mordenite zeolite-type catalyst that has an Si/Al molarratio of 57 was tested for the propene oligomerization reaction, afterbeing shaped as balls with an alumina binder. The catalyst that is usedis shaped in spherical balls that are 3 mm in diameter.

The feedstock that is used for this test is a feedstock that is obtainedfrom steam cracking that contains 94% by weight of propene and 6% byweight of propane.

The conditions were selected so as to optimize the formation of thediesel fraction in the oligomerate produced.

The operating conditions are as follows: Temperature of the feedstock atthe inlet of the reactor 210° C. Pressure 5.5 MPa VVH 0.7 h⁻¹

The volumetric flow rate of feedstock per volume of catalyst (VVH) wascalculated based on the total catalyst mass in the two reaction zones.The addition of fresh and regenerated catalyst is done so as to keep astable conversion in the two reaction zones.

20% of the spent catalyst that is obtained from the upper reaction zonethat is replaced by regenerated catalyst in an identical amount is drawnoff to increase the catalytic activity in the lower reaction zone.

The temperature of the cooling liquid is regulated so that the reactiontemperature at the inlet of the second reaction zone is equal to 210C.The cooling fluid that is used is water that is introduced at 25° C.

The results that are obtained are reported in Table 1. TABLE 1 ZeoliteMOR Si/Al Molar Ratio 57 Reaction zone inlet temperature (3b) (° C.) 210Reaction zone outlet temperature (3b) (° C.) 227 Reaction zone inlettemperature (3a) (° C.) 210 Reaction zone outlet temperature (3a) (° C.)225 C5+ oligomer (% by weight) 86.5 Diesel fraction (>180° C., % byweight) 81.2 Engine cetane number* 38*After hydrogenation

The use of the reactor according to this invention, in particular forthe oligomerization reaction of olefinic feedstock ranging from C3 toC6, provides several major improvements:

-   -   The reactor is compact while having a high catalytic volume and        an integrated heat exchanger. Its cost as well as its        installation cost are relatively low.    -   The addition of new or regenerated catalyst in zone (3 b) makes        possible, as a variant, an at least partial rebalancing of the        catalytic activity between the reaction zones, which is        favorable to the yield of the diesel fraction.    -   The continuous regeneration system of a portion of the catalyst        makes it possible, as a variant, to operate without having to        stop the unit to change the catalyst.    -   The heat exchange zone that is located between the two reaction        zones makes possible an improvement of the homogeneity of the        temperature in the two reaction zones.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forthuncorrected in degrees Celsius and, all parts and percentages are byweight, unless otherwise indicated.

The entire disclosure of all applications, patents and publications,cited herein and of corresponding French application No. 04/11959, filedNov. 9, 2004 is incorporated by reference herein.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A reactor of elongated shape along an essentially vertical axis, saidreactor comprising a cylindrical shell and several vertically-stagedcatalytic reaction zones in said cylindrical shell, whereby said reactoris adapted to the axial circulation of a reaction fluid serially in eachof said zones and comprises means (100) for introducing and means (101)for evacuating said reaction fluid, means (102) for intake of fresh orregenerated catalyst at the top of the reactor, and means (105) forevacuating spent catalyst in the lower portion of the reactor, saidreactor comprising: an upper reaction zone (3 a) filled with granularcatalyst, with a section that is essentially identical to that of thecylindrical shell on a portion of its height, directly connected via aconstriction zone to a reaction zone (3 b) that is also filled withgranular catalyst and with a section that is essentially identical tothat of the cylindrical shell on a portion of its height, located justbelow the upper reaction zone (3 a), whereby said reaction zones (3 a)and (3 b) are two successive reaction zones that are directly connectedby a reaction effluent path, and by a catalyst path from zone (3 a) tozone (3 b) through said constriction zone, whereby zone (3 a) isconnected at its upper portion, directly or indirectly, to said fluidmeans (102) for feeding fresh or regenerated catalyst, whereby zone (3b) is connected at its lower portion, directly or indirectly, to saidmeans (105) for evacuating spent catalyst, whereby the reactor, placedat the constriction zone between this constriction zone and thecylindrical shell of the reactor, also comprises a heat exchanger (8)for heating or cooling reaction fluid circulating between zones (3 a)and (3 b).
 2. Reactor according to claim 1, in which zone (3 a) in itsupper portion comprises an essentially conical convergent that comprisesperforations for the path of reaction fluid, connected to a channel (2b) with a reduced diameter relative to that of the reactor, whereby thischannel delimits at least a portion of the constriction zone.
 3. Reactoraccording to claim 2, in which said channel (2 b) has a diameter ofbetween 1% and 50% of the diameter of the reactor at the constrictionzone.
 4. A process comprising passing a hydrocarbon feedstock into areactor according to claim 1 and conducting a reaction therein.
 5. Aprocess according to claim 4 comprising oligomerizing olefinicfeedstocks having 2 to 12 carbon atoms in the presence of anoligomerization catalyst.
 6. A process according to claim 5, in whichthe pressure is between 0.1 and 10 MPa, the temperature is between 40and 600° C., the hourly volumetric flow rate VVH is between 0.01 and 100h⁻¹, and in which the catalyst circulates in each reaction zone at aspeed of between 1 cm/hour and 200 cm/hour.
 7. A process according toclaim 4, in which the operating conditions are selected: temperature,pressure, VVH, so as to limit the temperature variation in each of thereaction zones to one or more values between 2° C. and 50° C.
 8. Aprocess according to claim 5, in which the operating conditions areselected: temperature, pressure, VVH, so as to limit the temperaturevariation in each of the reaction zones to one or more values between 2°C. and 50° C.
 9. A process according to claim 6, in which the operatingconditions are selected: temperature, pressure, VVH, so as to limit thetemperature variation in each of the reaction zones to one or morevalues between 2° C. and 50° C.